The invention relates to the use of resiniferatoxin (RTX) for treating joint pains and, more particularly, to a method for treating joint pains that involves applying said agent in the intracapsular space or joint capsule of the joint.
Pain, emanating from joints, frequently has its origin in the area of the joint capsule or in the area of the bone in the vicinity of a joint. In this connection, many analogies may come into consideration, such as arthrotic or arthritic forms of a disease, mechanical or other irritation of bone surfaces in the vicinity of a joint, irritation or injury to the ligament structures of joints, infections, autoimmune processes, etc. In all cases, which are of interest within the scope of this invention, the resulting pain emanates from nociceptive nerve fibers in the region near the joint. Nociceptive fibers are also referred to as C fibers and A delta fibers. If an analgesic substance (such as a local anesthetic or morphine) is injected into a joint so diseased, the symptoms of the patient are alleviated. However, the substances, customary at the present time, act for only a limited period, so that the symptoms generally return.
In general, the following methods are used at the present time for the treatment of painful, diseased joints:                physiotherapy/movement therapy        systemic analgesic/antiphlogistic therapy (etc.)        local analgesic/antiphlogistic methods (etc.)        surgical methods        arthroscopic: debridement, joint toilette, etc.        open/mini-open joint replacement, joint reinforcement, etc.        
A series of known substances for the treatment of painful, inflamed joints has already been proposed in the literature, especially                osmic acid or radioactive substances, such as technetium 99, which lead to synoviorthesis,        injection of local anesthetics, hyaluronic acid preparations (etc.)        injection of antiphlogistic agents        injection of contrasting agents for joint diagnosis        joint flushing for joint toilette        chemical, thermal, electrical or surgical ablation of the nerves, which look after the joints.        
All previously used substances and methods lead to only a relatively brief or incomplete freedom from pain or cause lasting damage to the joint.
For example, the known method of synoviorthesis has the disadvantage of destroying the molecular structures, especially of denaturing the proteins, which act as initiators of inflammation in the process of arthritis and, partly also in the development of arthroses. Moreover, a fibrosis of the joint capsules is formed, which is less likely to become inflamed and accordingly also is less painful. At the same time, due to the fibrosis of the joint, which occurs during the synoviorthesis, the hyperemia, which is generally present and also to be treated, is decreased, resulting also in therapeutic benefit. However, the fibrotic scarring after synoviorthesis may lead to decreased mobility of the joint, as well as to a decreased production of synovial fluid and to a destruction of the joint cartilage. This undesirable fibrosis of the joint capsule should be avoided and only the sensitive innervation of the joint should be switched off.
The EP-B 0 998 288 of CAMPBELL discloses the use of capsaicin and analogues thereof (simultaneously or sequentially) with a local anesthetic. Local anesthetics are intended to prevent the burning pain during the injection of RTX. If the local anesthetics have an antagonistic effect with respect to capsaicins, the concentration of capsaicins, when used in combination with local anesthetics, must be higher than when capsaicin is used alone, in order to achieve the desired pain therapy. As side effects, capsaicins bring about hyperemia and inflammation reactions of the tissue.
U.S. Pat. No. 4,997,853 of BERNSTEIN discloses the use of capsaicin together with a local anesthetic having topical activity for the treatment of topical pain syndromes.
Admittedly, the use of capsaicins without local anesthetics is known for systemic use (intraperitoneal, subcutaneous, intravenous, etc. administration) or for regional use (epidural, intrathecal, transcutaneous administration or as a regionally selective nerve block), however, always in combination with general anesthesia of the experimental animals. However, it is a decisive disadvantage of a regional or systemic use that not only the affected region is treated, but also the asymptomatic, adjacent regions.
Admittedly, the use of capsaicins in the bladder (intravesical) without local anesthesia is also known. However, the agent is used here only topically and is not injected through a skin barrier.